Despite making an instant impact upon his arrival at United in 2010, Hernandez, 26, has struggled for first-team football in recent seasons, with new manager Louis van Gaal preferring Wayne Rooney and Robin van Persie up front.

The Mexico international has been linked with a number of clubs this summer, including Valencia and Juventus, but has reportedly opted to join Madrid, who view him as a perfect back-up to Karim Benzema.

Most Goals as a Substitute
Top 5 European Leagues, Last 5 Seasons

1) Javier Hernandez (Guadalajara, Man United) - 14

2) Edin Dzeko (Wolfsburg, Manchester City) - 13

3) Souleymane Camara (Montpellier) - 13

4) Victor Anichebe (Everton, West Brom) - 10

5) Giampaolo Pazzini (Sampdoria, Inter Milan, AC Milan) - 10

Hernandez was a feature on the bench during David Moyes' ill-fated tenure at Old Trafford and has not seen much game time under Van Gaal this term.

During the 2013-14 season, the striker played just 855 minutes in the Premier League and 1,435 minutes in cup competitions, scoring nine goals overall.

Under Van Gaal, Hernandez has played just 45 minutes so far in the league and one full match in the Capital One Cup -- United's 4-0 humbling at MK Dons.